dt-bindings: gpu: mali-utgard: add Amlogic Meson8 and Meson8b compatible

Add a compatible string for the Mali-450 GPU on Amlogic Meson8 and
Meson8b SoCs. Meson8 uses an "MP6" variant with six pixel processors
while Meson8b (as cost-reduced SoC) uses an "MP2" variant with two pixel
processors. Both have a reset line to bring the GPU into a well-defined
state.
Signed-off-by: NMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NKevin Hilman <khilman@baylibre.com>

Documentation/devicetree/bindings/gpu/arm,mali-utgard.txt

@@ -13,6 +13,8 @@ Required properties:
       + allwinner,sun8i-h3-mali
       + allwinner,sun50i-a64-mali
       + allwinner,sun50i-h5-mali
+      + amlogic,meson8-mali
+      + amlogic,meson8b-mali
       + amlogic,meson-gxbb-mali
       + amlogic,meson-gxl-mali
       + rockchip,rk3036-mali
@@ -82,6 +84,10 @@ to specify one more vendor-specific compatible, among:
     Required properties:
       * resets: phandle to the reset line for the GPU
 
+  - amlogic,meson8-mali and amlogic,meson8b-mali
+    Required properties:
+      * resets: phandle to the reset line for the GPU
+
   - Rockchip variants:
     Required properties:
       * resets: phandle to the reset line for the GPU